The purpose of this study is to evaluate the safety and efficacy of losigamone 1,500 mg per day and 1,800 mg per day compared to placebo for the management of inadequately controlled partial seizures when added to treatment with other AEDs in double blind randomized fashion. To determine the incidence of side effects of the two doses compared to placebo. To determine the pharmacokinetic-pharmacodynamic relationship of the two losigamone doses by comparing mean plasma levels to seizure control. To determine any evidence of clinically significant interaction between losigamone and concurrent AEDs.